not sure but . . .
check my page, click menu #13 and look at pin A-3: "phone mute: ground to activate".
Start from there and check it out by measuring the pin's voltage and ground it thru a small value resistor (10 ohms). Measure voltage drop and calculate current thru resistor.
If ok, then ground it without resistor. Radio should mute.
Regards . . . . JimF
'94 S500 Cpe
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